The use and manufacture of enteric dosage forms are well known to skilled personnel. Such dosage forms have been explained and reviewed in reference works, e.g., in Remington's Pharmaceutical Sciences, 18th edition, Mack Publishing Co., Easton, Pa. (1990). Enteric dosage forms are desirable, either to protect the content of the dosage form from the gastric conditions or to protect the gastric tissue from an irritant material contained in the enteric dosage form. A further use for enteric dosages is prevention of a lasting, unacceptable mouth odor resulting from ingestion of substances like garlic or fish oil. Enteric dosage forms are also used to provide slow or delayed release of a substance.
To fulfill the compendium definition requirement for enteric or gastro-resistant preparations, these preparations have to pass specific compendia tests. The enteric or gastro-resistant property is obtained only if the enteric dosage form does not dissolve or disintegrate in gastric acidity for a specified amount of time (usually two hours in 0.1 N hydrochloric acid at 37° C.). Further, the enteric dosage forms must release their contents in simulated intestinal environments (e.g., in buffers of pH values at about 6.8 within certain time periods). Detailed evaluation techniques are described in national and international pharmacopoeia such as United States Pharmacopoeia.
The majority, if not all, of the enteric dosage forms currently in use are produced by a film-coating process, where a thin film layer of acid-insoluble (enteric) polymer is accumulated on the surface of an pre-manufactured dosage form. Dosage forms coated in this manner have been mainly tablets and, to a lesser extent, hard or soft capsules. The enteric coating method involves spraying of an aqueous or organic solution or a suspension of enteric polymers onto tumbling or moving tablets or capsules, accompanied by drying using hot air.
Enteric dosage forms made by coating suffer from various process-related problems and defects that affect their performance or appearance. For example, “orange peel” surface formation, also known as surface roughness, mottling, or lack of surface homogeneity may result. And more seriously, coat integrity failure may occur, such as in cases of cracking or flaking off of the coating. All coatings present inherent problems, including possible uneven distribution of the coating ingredients, which can easily happen under the multivariate coating process.
The foregoing problems of enteric coatings are shared by all enteric dosage forms such as tablets and capsules. However, the problems faced during coating of capsules are even more critical, due to the delicate and heat sensitive nature of the soft elastic capsule shell. Both hard and soft capsules can easily undergo agglomeration and distortion due to the heat-sensitive shell composition. Moreover, the smoothness and elasticity of the capsule surface make it difficult to form an intact adhering enteric coat without careful sub-coating step to improve the surface for coating. A further disadvantage of enteric coating for soft capsules is the loss of the normally shiny and clear appearance of capsule gelatin shells. The elegant, clear gelatin shell has been a significant reason for soft capsule popularity and acceptance. In addition to the undesirable surface texture modifications usually caused by coating, most accepted aqueous enteric polymer preparations result in opaque capsules.
While different attempts have been tried to improve the manufacture of enteric soft gelatin capsules via coating, the inherent disadvantages in the coating process amplify the necessity for a better way of manufacturing enteric soft capsules, ideally, without coating. Enteric coatings (both sub-coating and over-coatings) and enteric polymers are discussed or suggested generally in U.S. Pat. Nos. 4,518,433, 4,816,259, and 5,330,759. None of these references, however, teach or suggest the invention as set forth herein.